PSF Reconstruction: Part IThe PSF “Core” • Primary Goal: Derive PSFs for point source detection and PSF fitting photometry. • Secondary Goal: Derive PSFs to use in point source subtraction - can reduce signal from PSF by a factor of 1000 or more.
Data Set • IOC task IRAC 500 in Campaign R • Imaged 7th magnitude IRAC standard p73.0324, a 7.2 mag K0III star • Used HDR mode since there will be some saturation in Bands 1 and 2. • Observed stars at 25 positions on the array, with a 4x4 grid of dithers at each position spaced by 1.5” • 16 AORs resulting in 800 images per band
Data Reduction:1st iteration • PSFs are found and a centroid is measured in each image. • The data for each of the 25 position is separated. Typically there are sixteen 0.6 sec and 10.4 sec frames per position. • A 51x51 pixel region centered on the PSF is extracted. • For each of the 25 positions, the data are drizzled onto a grid with 0.3” pixels with a drop size of 0.5. Uses Richard Hook’s drizzle library linked to IDL.
Variations in the PSF(for Channel 1) Lower Left Upper Right
Data Reduction: Iteration II(work in progress) • Take PSF derived from interation 1. • Derive new centering using a least square fit of PSF with each image. • Compare drizzled PSF with each image to detect cosmic rays and reject. • Recombine with drizzle.
Dynamic Range in Channel 1 1e-4 Log 1e-5 5e-5
Finishing • Finish cosmic ray rejection and re-centering. • Produce next generation in all four channels. • Test in Source Extractor. • Re-run with cleaner data. • Try other reconstruction techniques (Fourier??)